It is known that the use of computers in a manufacturing environment is increasing at an ever accelerating rate. Whereas it was previously common to install one or two computers which interacted with remote peripheral sensors and the like, there is an increasing tendency to utilize computers, generally in the form of microprocessors, as close as possible to the events or environment being sampled or controlled.
Accordingly, along with this proliferation of computers there is now the need to network them so as to form a distributed control system. One distinct advantage with distributed processing is the desirability and ability to switch to a backup when, for example, the network or a primary computer goes down or malfunctions.
It is therefore important to have as much information on the secondary computer as the primary so that it can generally perform its function without interruption. Unfortunately, with the increasing use of computers, changes are made to the system on a much more pervasive and frequent basis.
Heretofore, backup databases, those databases which were used in the event of a primary system failure, were run in synchronization with essentially identical equipment running both copies in similar environments. Modifications to one database however, generally had to be made to the other databases and required at least some manual intervention. Accordingly, this required that all modifications had to be done at least twice. This is particularly problematic when complex modifications need to be done which thereby results in tedious duplicative work. Moreover, the chance of an error or discrepancy between the backup and primary databases was greatly increased.
There are a number of schemes which have tried to manage a network type system. One such example may be founded in U.S. Pat. No. 5,093,782 "Real Time Event Driven Database Management System" to Muraski et. al., issued Mar. 3, 1992 which attempts to speed up and simplify a database system. However, these systems generally require specialized hardware, unique architecture and the like and are therefore generally not "retrofitable" to existing systems.
Accordingly, it is advantageous and an object of the present invention to keep primary and backup databases synchronized without manual intervention. It is also desirable and yet another object of the present invention to produce a system which allows for hardware or network failure by one portion of the system without affecting the remaining portions.
It is still a further object of the present invention and is also desirable to produce a system which effectively allows for two or more different computers to have effectively identical databases while still allowing for communication between the two.
Still a further object of the present invention is to produce a redundant system which makes the backup database invisible or transparent to the user and which automatically accomplishes synchronization without any special effort on the part of the user.
It is also advantageous and another object of the present invention to produce a redundant network database system, comprising at least two computers, a communication link disposed between them so as to allow communication between the two computers and a means for sensing a change to a database and producing an indication thereof and a communications means for sensing the indication produced by the first means whereby the communication means updates the database of the remaining at least two computers.